Emollients are materials that are applied to the skin of subjects to produce softness or smoothness. They have been used for centuries in both cosmetic and pharmaceutical products. The original emollients were extracts or directly concentrated materials from plants or animals, while modern emollients also include partially synthetic (derivatives of natural products) or completely synthetic materials.
In addition to the feel of an emollient upon application to the skin, cosmetics and their ingredients must exhibit stability, both in storage and in use. The cosmetics must not deteriorate or separate in storage and use, and the individual ingredients should not decompose or otherwise undergo chemical changes that alter their desirable properties. One of the more common susceptibilities of products or components to ambient damage is from oxidation, and natural materials are clearly, through observation, susceptible to oxidation, as is commonly seen by browning of fruit exposed to air or the rancid smell of old vegetable oils. Many foods, food additives, cosmetics, fragrances, medicaments, and colorants are well known to be subject to damaging effects from oxidation.
The most frequent means of reducing the effects of oxidation (including light amplified or stimulated oxidation) include oxygen excluding packaging (e.g., bottles, cans, oxygen impermeable polymer wraps, and the like), chemical modifications of the ingredient to reduce its tendency toward oxidation while minimally altering its functional properties, and the addition of antioxidants to directly quench oxidative species before they oxidize the ingredient. Packaging controls are most effective where a product is to be used once, as when the package is opened, air is introduced into the container and the package provides no complete protection against contact with oxygen. Chemical modification of an ingredient offers more general protection, assuming that a modification can be devised that both substantially reduces the tendency towards oxidation and also maintains the functional properties desired in the selection of the underlying chemical. This can be an exhaustive task, with no guarantees of success.
The use of antioxidants offers a general approach to the oxidation problem for a wide variety of materials and fields including the protection of edible materials against premature oxidation. The use of antioxidants would appear to some to require little more than the appropriate selection of an antioxidant sold commercially for specific purposes to achieve a commercially viable product with a necessary level of oxidation resistance. However, antioxidants may have and often display unique interaction with other ingredients and with the primary component on either a physical level (by not blending with the other materials), on a chemical level (by reaction with active ingredients), or both. It is therefore necessary, with some compositions that require antioxidant protection, to conduct extensive research with no assurance of success. There are also such a wide variety of classes of antioxidants and so many variants within the classes that a search for an appropriate antioxidant is a highly problematic search, and the desire for the best antioxidant assures a time consuming process.
Among the more common classes of antioxidants are free-radical terminators, particularly those with available hydrogens from phenolic hydroxyl groups. Within that single class are the subclasses of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT), hydroquinones (such as tertiary-butylhydroquinones, and propyl gallate). Reducing agents or oxygen scavengers encompass another class of antioxidants and includes ascorbic acid (vitamin C) and its derivatives (such as esters of ascorbic acid, such as ascorbyl palmitate); sulfites (such as sulfur sulfite, alkali metal sulfites, and bisulfites, including alkali metal bisulfites); glucose oxidases (including catalase); erythorbic acid and its derivatives. Chelating agents comprise another class of materials that have been used to address problems with potentiators of oxidation and include citric acid (and its derivatives), polyphosphages, and aminopolycarboxylic acids (such as ethylenediaminetetraacetic acid (EDTA). Finally, there are other antioxidant classes with less general areas of use.
The use of polyglycerol esters as oil in water (o/w) emulsifiers for cosmetic formulations is described, for example, in J. Soc. Cosmet. Chem. 28, 733-740 (1977) and in Fette, Seifen, Anstrichmettel 88, 101-106 (1986). In addition, the use of selected polyglycerol fatty acid esters as cosmetic emulsifiers is claimed in DE-A1 40 05 819 and DE-A1 40 23 593 (BASF). However, in cases where the esters based on unsaturated or saturated fatty acids mentioned in these documents are used, it has been found that the resulting emulsions are not always sufficiently stable in storage. The invention of that reference relates to cosmetic and/or pharmaceutical formulations that are characterized in that they contain monoesters of triglycerol with saturated C16-C18 fatty acids as emulsifiers, the monoester content being from 30-50% by weight. It was asserted that it was surprising that the degree of self-condensation of the oligoglycols in conjunction with the nature of the fatty acid and the percentage content of monoesters has a bearing on the properties of the resulting emulsifiers. That invention includes, in particular, the observation that the establishment of a percentage monoester content of 30-50% in the emulsifiers according to the invention leads to a significant improvement in stability compared with otherwise known products of the prior art.
In spite of this, there is a present and continuing need for a class of compositions comprising oils and waxes that exhibit extended stability relative to unadulterated oils and waxes alone.